The present invention generally relates to methods and apparatus for determining the fluid level of a container, such as an accumulator, and more specifically, to methods and apparatus for determining the fluid level of a container without the need for either electrical power or a direct line of sight to the container.
Accumulators are frequently used on military and commercial aircraft to accommodate the thermal expansion of coolant and hydraulic fluids. During aircraft servicing, maintenance personnel need to ascertain if the respective liquid loop contains the appropriate fluid level. Often, the accumulator is located in an inconvenient space for visual inspection and there is no aircraft electrical power available to operate a level sensor.
U.S. Pat. No. 943,596, issued to Hans, discloses a method of indicating the height of liquid in a tank. A float is attached to a cable and as the float rises and falls, the cable moves in a linear direction. The opposite end of the cable is wrapped around a drum, which turns linear cable motion into rotational motion of the drum. Additional gearing eventually translates the rotational motion of the drum into rotational motion of a dial indicator, allowing visual indication of the liquid level. The indicator housing is attached to the float housing, requiring a visual line of sight to make a liquid level reading. This requirement of a visual line of sight, as used by Hans, may not be useful in applications such as an aircraft, where components are closely assembled, possibly blocking many sight lines to liquid containers.
U.S. Pat. No. 2,074,959, issued to Guest, discloses a fuel tank gauge that may be remotely located. In the Guest patent, the liquid movement is transferred to linear motion of either a cable or a chain. The cable of Guest is located in a conduit that extends to the gauge. The cable moves linearly in the conduit, wherein the linear motion of the cable is translated to rotary motion of the gauge. This linear cable movement requires a relatively linear path from the tank to the gauge in order to avoid the linearly moving cable from getting stuck in the conduit due to kinking or the like.
U.S. Pat. No. 2,522,988, issued to Caddell, discloses a method of indicating oil level using a float that drives a chain in a linear motion. The chain is looped over a sprocket causing the sprocket and attached shaft to move in a rotary motion. One end of the shaft may be connected to an indicator assembly. The shaft of the Caddell patent appears to be a rigid shaft, thereby requiring the indicator to be located linearly away from the oil tank. In situations where there is no line of sight to the tank, there would usually also be no direct linear line for a shaft to run to drive a remote indicator, as would be required in the Caddell gauge.
As can be seen, there is a need for improved methods and apparatus for determining the fill level of a container, such as an accumulator, at a location more convenient for maintenance and without the need for electrical power or a direct line of sight to the accumulator.